This invention relates to hydraulic cylinders and, more particularly, to cylinders for use in mechanical systems having confined areas, or where reduced cylinder size is desired.
In mechanical systems where limited space is available for an actuating hydraulic cylinder, three basic methods of reducing the space occupied by the cylinder have commonly been applied. One method includes the use of a telescoping cylinder, which is a cylinder having multiple rods extending in one direction having progressively smaller diameters so that the rods can be contained within one another. Inherent disadvantages associated with telescoping cylinders is that because the cylinders are contained within one another, the outermost cylinder can be quite large in diameter. Consequently, the use of this type of cylinder is unavailable for systems where an extremely limited space is available. Telescoping cylinders are also difficult to seal because of their complex design, they require a large number of seals. Furthermore, besides being very costly, telescoping cylinders are very weak in the retract mode.
A second method commonly utilized for actuating hydraulic cylinders in confined areas is by using two opposing cylinders with housing connected together in a side by side arrangement wherein the cylinder rods extend in opposite directions. This method has also proven to be ineffective because opposing cylinders with housings connected together produce an undesirable rotating torque when the cylinders are actuated. Additionally, if the cylinder rods are placed in parallel to one another rather than in an aligned arrangement, an undesirable bending moment is applied to the rods.
A third method for actuating hydraulic cylinders in a limited space is by mounting the cylinders at an angle skewed from the actual direction of mechanism actuation, such as in a criss-cross mount or scissors arrangement. Criss-cross and scissors assemblies, however, have a variety of inherent problems with limited stroke capability, inconsistent forces throughout the stroke, and undesirable high loads on mechanism joints. Therefore, a need exists for an improved hydraulic cylinder that eliminates the problems associated with previous cylinder designs, which can be utilized in mechanical systems where limited space is available and which are easy to install and maintain.